@book {R{\"u}ther 1936, title = {Der heilige Bruno von K{\"o}ln, der Kart{\"a}user}, series = {Lebensschule der Gottesfreunde}, number = {22}, year = {1936}, pages = {48}, address = {Meitingen}, keywords = {biographiae, Bruno Cartusiensis (biographia)}, author = {R{\"u}ther, Josef} }